I know that there are other stretch tapes around, but I would instantly buy a Cathe stretch tape. Not yoga, just a really good, relaxing, effective stretch for a rest day or tired day.
Lots of people have mentioned CTX2, so how about a stretch workout as part of this kind of series. Or, if there were 6 workouts, there could be a bonus 30-minute stretch for the 7th day. Just a thought...